It is important for tires, particularly high performance tires and race tires, to have good traction for the running surface of the tire. It is also important for tires to have good wet traction on wet road surfaces.
In practice, rubber compositions for tire treads typically contain a combination of zinc oxide and stearic acid which forms zinc stearate in situ within the rubber composition. Zinc stearate itself is a relatively slippery soap in the presence of water which gradually migrates and blooms to the running surface of the tire to thereby reduce the tire tread's wet traction on wet road surfaces.
Accordingly, a challenge has been undertaken to evaluate the feasibility of providing an alternative to the zinc stearate soap contained in the tire tread for the running surface of the tire tread particularly where enhanced wet traction for the tread running surface is desired.
For such challenge, the feasibility of replacing at least a major portion (greater than 50 percent), or all, of the stearic acid in the tread rubber composition with rosin acid is evaluated with a resultant formation of zinc rosinate in situ within the tread rubber composition instead of the zinc stearate.
While it is contemplated that the zinc rosinate is also a soap, it is in the nature of a sticky soap in the presence of water as compared to the aforesaid slippery zinc stearate soap, particularly when the tread surface is wet in the sense of traveling over a wet substrate.
In the description of this invention, the terms “compounded” rubber compositions and “compounds”; where used refer to the respective rubber compositions which have been compounded with appropriate compounding ingredients. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The amounts of materials are usually expressed in parts of material per 100 parts of rubber by weight (phr).